Multimessenger Emission by Magnetically Arrested Disks and Relativistic Jets of Black Hole X-Ray Binaries

Abstract Black hole X-ray binaries (BHXBs) are observed in various wavelengths from radio to GeV gamma rays. Several BHXBs, including MAXI J1820+070 and Cygnus X-1, are also found to emit ultrahigh-energy (UHE; photon energy > 100 TeV) gamma rays. The origin and production mechanism of the multiwavelength emission of BHXBs are under debate. We propose a scenario where relativistic particles from magnetically arrested disks (MADs), which could form when BHXBs are in quiescent or hard states, produce UHE gamma rays, while electrons in the jets produce GeV gamma-ray emission. Specifically, magnetic turbulence in MADs heats up and accelerates electrons and protons, while magnetic reconnection in jets accelerates electrons. Sub-PeV gamma rays and neutrinos are produced when relativistic protons interact with thermal protons and the radiation emitted by thermal electrons in the disk. We discuss the perspectives of observing sub-PeV multimessenger signals from individual BHXBs. Finally, we evaluate the integrated fluxes of the quiescent and hard-state BHXB population and find that BHXBs may contribute to the Galactic diffuse emission above ∼100 TeV.